JP7143314B2 - Method and apparatus for aligning two optical subsystems - Google Patents

Description

Aligners are used in the semiconductor industry to align multiple substrates, in particular wafers, to each other and thereby bond them together in further process steps. The joining process is called bonding. Mutual alignment of the substrates is performed by alignment marks provided on the surfaces of the substrates. The alignment marks on the opposing surfaces of the opposing substrates are in particular complementary to each other.

An alignment process in which alignment marks are provided on the surfaces of the substrates to be bonded is referred to as face-to-face alignment. As long as the substrates are opaque to the electromagnetic radiation to be measured, a method needs to be developed to measure the marks before the substrates are brought close together.

A practice that has been practiced for a very long time has been to insert a camera between the substrates and remove the camera before approaching the substrates. This had many drawbacks. Firstly, it results in the camera being contaminated by particles, at least on the lower substrate, and secondly, in order to position the camera between the two substrates, the distance between the substrates must be chosen relatively large. did not become. Due to the long distance, the distance traveled when the two substrates approach each other after removal of the camera is also very long, and the substrates are laterally shifted as they approach each other, thus leading to their optimal mutual alignment. It had the drawback of deviating from alignment.

An improved form of face-to-face alignment is the aligner of publication US Pat. No. 6,214,692. The disclosed aligner completely omitted the use of a camera interposed between the substrates. Instead, two optics groups, each with two optics facing each other, are used to create a system with two reference points against which the substrates can be positioned relative to each other. It had been. The reference point was the intersection of the optical axes of the two mutually opposing optical systems. A corresponding process for calibrating an optical system of this kind is fully disclosed and was explained.

Problems with the prior art, in particular with the calibration method according to figures 2c and 2e of publication WO2014202106 or figures 5a and 5b of publication WO2015082020, are the This means that a calibration substrate is required to serve as a reference when performing optical axis calibration. The upper and lower optics are specifically calibrated to alignment marks on transparent substrates. That is, the left optical axis is adjusted to the left focus and the right optical axis is adjusted to the right focus. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and a system which do not have the drawbacks of the prior art and in particular allow two optical systems to be aligned or calibrated with respect to each other in a simple manner.

This task is solved by the features of the independent claims. Advantageous developments of the invention are described in the dependent claims. Also included within the framework of the invention are any combinations of at least two of the features mentioned in the description, claims and/or drawings. Where ranges of values are specified, values within the stated boundaries are also disclosed as boundary values and any combination may be claimed.

The invention describes in particular how the two image planes of two mutually opposing optical systems and/or the optical axes of the two optical systems can be aligned with each other.

Advantageously, the use of a calibration substrate according to publication WO2014202106 can be omitted.

According to the present invention, a method is provided for aligning two optical subsystems of an optical system which are arranged oppositely, in particular arranged one above the other, the method comprising the steps of Are:
- projecting the alignment mark onto the image plane of the first optical subsystem, in particular of the lower optical subsystem;
- projecting the alignment marks from the first image plane onto the sensitive surface of the second optical subsystem, in particular of the upper optical subsystem;
- mutually aligning the optical subsystems so that the projection of the alignment marks at the depth of field of the sensitive surface is imaged to an ideal position.

The depth of focus and/or depth of field of all optical elements, in particular optical systems, is between 1 nm and 10 mm, especially between 10 nm and 1 mm, more preferably between 50 nm and 500 μm, particularly preferably between 500 nm and 250 μm. between 1 μm and 100 μm, very preferably between 1 μm and 100 μm.

In one preferred embodiment, the light for illuminating the alignment marks comprises at least one light source, in particular a lamp, preferably a halogen lamp, more preferably an LED, particularly preferably a laser light source, and at least one mirror. and/or to the first optical subsystem and/or the second optical subsystem. With such an external light source a particularly bright illumination of the alignment marks can advantageously be achieved.

According to one further preferred embodiment, at least one point of the optical subsystem, in particular the first camera and/or the mirror, ambient light is coupled in for illuminating the alignment marks, in which case preferred is not provided with a shield for the optical subsystem. This advantageously achieves illumination of the alignment marks without an additional external light source.

According to one further particularly preferred embodiment, an alignment mark, which in particular comprises an LED field and/or is formed as a mask, is projected onto the first camera chip of the first camera by the alignment mark projection system. 1 is projected onto the sensitive surface. This advantageously eliminates the need to introduce alignment marks into the camera chip.

According to another preferred embodiment, the optical subsystem includes two optical systems positioned opposite each other, the image planes and/or optical axes of the two optical systems being aligned with each other. be. This advantageously results in a particularly efficient alignment of the optical subsystems or optics.

According to another preferred embodiment, at least the optical system is part of an apparatus for aligning substrates, in particular wafers. This advantageously provides a significant improvement in apparatus for aligning substrates.

According to another preferred embodiment, the method according to the invention has the following sequence:
- arranging an alignment mark near and/or on the first sensitive surface of the first camera chip of the first camera and/or the first camera chip of the first camera; projecting alignment marks onto one sensitive surface;
- projecting the alignment marks from the first camera chip, via a first optical subsystem having a first optical system, onto a first image plane located between the optical systems;
- projecting the alignment marks from the first image plane onto the second sensitive surface of the second camera chip of the second camera via a second optical subsystem comprising a second optical system; ,
- in particular the optical system so that the projected alignment mark of the alignment mark is sharply imaged on the second camera and the position of the projected alignment mark coincides with the desired and/or ideal position; to each other.

According to another preferred embodiment, the optics are moved for alignment by mutual translational and/or rotational movements. This advantageously allows a particularly precise alignment to be achieved.

According to another preferred embodiment, the optical system is such that for alignment the first image plane of the first optical system is at the depth of field of the second object plane of the second optical system. approached to exist. This advantageously results in a particularly sharp imaging of the alignment marks.

According to one further preferred embodiment, alignment marks are provided directly on the first sensitive surface of the first camera chip of the first camera, in particular by lithographic methods. This advantageously results in a particularly efficient formation of the alignment marks.

According to one further preferred embodiment, an alignment mark comprising a collection of non-functioning pixels, in particular exhibiting a cross shape, is provided directly on the first sensitive surface of the first camera chip. A particularly simple production of the alignment marks is thereby advantageously achieved.

According to another preferred embodiment, the alignment mark is provided on a separate marking plate on the first camera chip of the first camera, where the alignment mark and the first camera chip of the first camera chip are aligned. The distance from one sensitive surface is less than 1 mm, in particular less than 100 μm, more preferably less than 10 μm, particularly preferably less than 1 μm, very preferably less than 0.1 μm. This advantageously eliminates the need for machining the camera chip to form the alignment marks.

Another subject of the present invention is a method for two optical systems arranged opposite, in particular one above the other, by a method according to any one of the method claims in the patent claims. Regarding the system for aligning the optical subsystem, this system has the following components:
- a first camera with a first camera chip for projecting alignment marks onto the image plane of the first optical subsystem, in particular of the lower optical subsystem;
- means for projecting alignment marks from the first image plane onto the sensitive surface of the second optical subsystem, in particular of the upper optical subsystem;
- Means for mutually aligning the optical subsystems, thereby allowing the projection of the alignment marks in the depth of field of the sensitive surface to be imaged in an ideal position.

Embodiments relating to the method also relate to the system according to the invention.

Another object of the present invention is in the vicinity of the sensitive surface of the camera chip and/or for a system and/or method according to any one of the system and/or method claims in particular. The present invention relates to a camera chip having alignment marks on its sensitive surface. The description of the method also relates to the camera chip according to the invention.

Optical System Embodiments in accordance with the present invention relate to an optical system consisting of at least a first lower optical subsystem and a second upper optical subsystem. In the following description of this disclosure, when considering preferred structures, all entities will be denoted by "upper" or "lower" only. The lower optical subsystem and the upper optical subsystem have at least one optical element, in particular a plurality of optical elements. Optical elements include, in particular:
mirrors, especially
〇Plane mirror 〇Convex mirror 〇Concave mirror lens 〇Convex lens ・Both convex lens ・Plane convex lens ・Convex lens 〇Concave lens ・Both concave lens ・Plane concave lens ・Convex lens 〇Fresnel lens Prism diffraction element 〇Diffraction grating etc.

The mirrors are preferably cold light mirrors (hereinafter also referred to as cold mirrors) that filter out infrared light from the in-coupled light in order to prevent unnecessary and undesired heating of the optical system. In particular between 1000 μm and 0.8 μm, especially between 750 μm and 0.8 μm, more preferably between 500 μm and 0.8 μm, particularly preferably between 100 μm and 0.8 μm, very preferably 50 μm and 0 μm. Light with wavelengths between 0.8 μm is filtered.

An embodiment according to the present invention for projecting an object to be projected, in particular an alignment mark, from the lower camera chip, in particular from the sensitive surface of the lower camera chip, onto the upper camera chip, in particular the sensitive surface of the upper camera chip. An exemplifying explanation will be given. It is also conceivable for the alignment marks to be projected from the upper camera chip, in particular from the sensitive surface of the upper camera chip, onto the lower camera chip, in particular on the sensitive surface of the lower camera chip. For the sake of completeness, and also referring to the extreme case, alignment marks are provided on every camera chip, and in particular on the sensitive surface of every camera chip, each alternately and respectively on the opposite camera. projected onto the chip or onto the sensitive surface of the camera chip on the opposite side, respectively. As will be seen from the description below, only the projection direction is important for producing the effect according to the invention.

In the following description of this disclosure only the exemplary case where the lower alignment marks are projected onto the sensitive surface of the upper camera chip will be discussed.

An embodiment according to the invention presupposes a lower camera chip having alignment marks in the vicinity of its sensitive surface, in particular directly on its sensitive surface. The alignment marks may actually exist, or the alignment marks are simply alignment marks projected onto the bottom camera chip. In the latter case, the alignment marks are projected onto the sensitive surface of the lower camera chip by an alignment mark projection system. This embodiment is the most preferred of all embodiments. Because no camera chip with corresponding alignment marks is required, the alignment marks can be projected onto any commercially available chip.

In a first embodiment according to the invention, alignment marks are made directly on the bottom camera chip. In particular, alignment marks are provided on the sensitive surface of the lower camera chip. The manufacture of alignment marks on the bottom camera chip is particularly desirable to be performed by the chip manufacturer and is almost impossible to be performed by the customer purchasing such a chip. It is also conceivable to dismantle the obtained lower camera chip and completely expose the sensitive surface of the lower camera chip. It is also conceivable to subsequently reassemble the disassembled lower camera chip by providing corresponding lower alignment marks using known lithographic methods. However, removing the protective glass for the sensitive surface often destroys the camera chip, especially the sensitive surface of the camera chip itself, so removal of the protective glass is usually carried out non-destructively. it is impossible to

In a second preferred embodiment according to the present invention, the lower alignment marks are not made directly on the lower camera chip, but can be mounted on the sealed lower camera chip via fixing means. It is made on a support (also referred to as a marking plate) that can be used. In order to ensure that the lower alignment mark is in the depth of field of the lower recording camera, which is located on the opposite side of the optical path, the lower alignment mark is positioned over the sensitive area of the lower camera chip. Note that it must be as close to the face as possible.

The distance between the alignment marks and the sensitive surface is less than 1 mm, in particular less than 100 μm, more preferably less than 10 μm, particularly preferably less than 1 μm, very preferably less than 0.1 μm. Since sealed camera chips can in most cases be dismantled relatively easily, except for the last cover plate of the photosensitive area, a support according to the invention with alignment marks in the vicinity of the photosensitive area. Positioning can be achieved.

In a third, somewhat preferred embodiment of the invention, the lower alignment marks are projected onto the photosensitive surface of the lower camera chip. This has the advantage that any arbitrary bottom camera chip can be provided with bottom alignment marks. In order for the bottom alignment marks projected on the bottom camera chip to be in ideal positions, the calibration of the bottom alignment marks on the bottom camera chip projected by the alignment mark projection system should be can be projected onto the upper camera chip through the optical path of the optical system, thereby bringing the two camera chips into alignment with each other.

Now, in an essential inventive aspect, the lower alignment marks of the lower camera chip are projected onto the photosensitive surface of the upper camera chip, which is located on the opposite side of the optical path from the lower camera chip. In order to achieve an accurate and sharp projection of the lower alignment mark on the upper camera chip, i.e. to obtain a sharply projected upper alignment mark, the optical elements, in particular the lower optical subsystem and the upper optical subsystem, must be calibrated to each other. Completion of calibration is confirmed by the presence of the projected top alignment mark on the top camera chip at the ideal position.

The two optical subsystems each have mutually conjugate object and image planes. A conjugate surface is understood to be a surface that is arithmetically connected to one another by the imaging rules of the Fourier transform. If the two planes are perpendicular to the optical axis of the optical beam path, imaging an object from object space into image space and vice versa from image space into object space. Also, the two faces are conjugate to each other.

Exemplarily, considering the projection of the lower alignment marks of the lower camera chip onto the upper camera chip, the lower photosensitive surface of the lower camera chip is the first object plane.

The actual or projected alignment mark of the alignment mark projection system on the lower photosensitive surface of the lower camera chip lies, inter alia, in the object plane. Generally, the actual alignment marks need only be at a depth of field near the object plane.

The lower optical subsystem now projects those alignment marks onto its image plane. This image plane is the first lower image plane. This lower image plane lies in each case between two optical systems whose optical paths must be mutually calibrated. The second optical subsystem similarly has an optical surface between the optical systems. However, those optical surfaces now function as object planes and project the alignment marks of the photosensitive surface of the lower camera chip, projected onto the lower image plane, onto the second upper image plane of the upper optical subsystem. have a task. The upper image plane therefore coincides with the sensitive surface of the upper camera chip. The lower image plane and the upper object plane should be as congruent as possible so that the image of the alignment mark projected onto the lower image plane is also imaged onto the upper image plane as losslessly and particularly sharply as possible. must.

Based on the fact that the lower image plane of the lower optical subsystem and the upper object plane of the upper optical subsystem are generally not congruent, or even the depth of field of the respective other optical surface, the optical subsystem's In particular, changes in optical elements are required. This change requires in particular an adaptation by translational and/or rotational movement of the optical elements of the lower optical subsystem and/or the upper optical subsystem, in particular a change by translational and/or rotational movement of the optical system. The purpose of the embodiments according to the present invention is not only to project the lower alignment marks of the lower camera chip onto the photosensitive surface of the upper camera chip sharply, but also to achieve the theoretically desired ideal position of the projected alignment marks. It also means that the optical elements in the optical system are adapted until they match the correct position. Among other things, the same camera chip is used in the lower optical subsystem and the upper optical subsystem. Therefore, the ideal projected alignment mark position is in the same detector coordinate system that also has the alignment mark to be projected on the lower camera chip. The optical system is varied and adapted so that the mark lies within a freely selected tolerance range with respect to the ideal position.

Process The process according to the invention can be used to calibrate the optical system in particular in the devices of the publications US Pat. can be done. However, this does not limit the generality of the process. In general, the process according to the invention can be used to calibrate any two optical systems, especially fully automatically.

In a first process step according to the invention, two image planes are arranged such that the lower image plane lies at the depth of field of the upper object plane or the upper object plane lies at the depth of field of the lower image plane. The optical surfaces are brought closer together. In the first process step according to the invention, the projected left-hand top alignment mark or right-hand top alignment mark is not yet necessarily sharp. In particular, the two upper alignment marks may not necessarily yet be in the field of view of the upper camera. The field of view of the camera is between 10 μm and 50 mm, especially between 50 μm and 25 mm, more preferably between 100 μm and 15 mm, particularly preferably between 250 μm and 10 mm, very preferably between 300 μm and 5 mm.

In a second process step according to the invention, a change of the lower optical subsystem and/or the upper optical subsystem is performed such that at least two projected alignment marks are present in the field of view of the upper camera. A change of the lower optical subsystem and/or the upper optical subsystem is in particular by a translational movement and/or by a rotational movement of at least one optical element of the lower optical subsystem and/or the upper optical subsystem and/or interpreted as a functional change. In particular, a translational and/or rotational movement of the lower optics and/or the upper optics is understood here.

In a third process step according to the invention, a wedge error compensation between two optical surfaces or a reduction of the angle between the optical axes takes place. Wedge error compensation is performed such that at least one optical element in the lower optical subsystem and/or the upper optical subsystem is changed to reduce the tilt between the two optical axes of the two optical subsystems. In particular, wedge errors are reduced by rotation of at least one of the two optical systems.

In a fourth process step according to the present invention, after all alignment marks are in the field of view and depth of field of the top camera chip and the wedge error is sufficiently reduced, the projected alignment marks on the top camera chip are Precise alignment between the alignment marks is achieved by bringing them to ideal positions. This is done in particular by a translational movement and/or rotation of the lower optics and/or the upper optics.

In particular, the first to fourth process steps according to the invention can be performed in any order and/or simultaneously. The in particular simultaneous execution of all process steps according to the invention is ensured by corresponding firmware and/or hardware and/or software that allows the two optical subsystems to be algorithmically calibrated to each other, in particular fully automatically. . In particular, calibration can be performed automatically by a control loop.

The first to third process steps according to the invention are particularly coarse calibration process steps, which very rarely occur, especially after maintenance, construction or repositioning of embodiments according to the invention. , need only be fully implemented. After a coarse calibration has been performed, only a fine calibration with a fourth process step is often required over a longer period of time.

An optical system calibrated according to the invention can then be used for surface measurements. In particular, the system is suitable for aligning two substrates to each other. In one highly preferred embodiment, the system is used to align two substrates face-to-face with each other.

Another possibility for using the optical system calibrated according to the invention consists in the measurement of the top and bottom sides of a substrate or substrate stack. The optical system is used in this special case as part of a metrology tool. Simultaneous measurement of the top and bottom surfaces of a substrate or stack of substrates is often performed to measure the horizontal distance between two surface features.

Camera Chip The camera chip is configured in particular as an area detector. Among other things, the camera chip is a CCD detector, a CMOS detector, an analog detector, a four-quadrant detector or a so-called Position Sensing Device (PSD). The camera chip has a to 100 Hz. Here, the readout frequency is understood to be the number of complete interferograms that the camera chip can read out per second.

The horizontal pixel resolution of the camera chip is in particular higher than 10 pixels/cm, in particular higher than 100 pixels/cm, more preferably higher than 1,000 pixels/cm, particularly preferably 10,000 pixels/cm. higher, very preferably higher than 100,000 pixels/cm.

The vertical pixel resolution of the camera chip is in particular higher than 10 pixels/cm, in particular higher than 100 pixels/cm, more preferably higher than 1,000 pixels/cm, particularly preferably 10,000 pixels/cm. higher, very preferably higher than 100,000 pixels/cm.

The distance between two pixels is between 0.1 μm and 100 μm, especially between 0.5 μm and 50 μm, more preferably between 1 μm and 25 μm, particularly preferably between 2.5 μm and 10 μm, very preferably is 5 μm.

In one particular embodiment according to the invention, the optical system can have two cameras containing two different camera chips. The camera chips may, for example, differ in their size. On the contrary, in that case, the use of alignment marks can be omitted. Calibration according to the invention is performed in such a way that the contours of one camera chip are projected onto the respective other camera chip. The optics that provide the scaling allow the camera chip from which the projection takes place to be congruently imaged onto the surface of the other camera chip. That is, in general, an affine transformation of one camera chip to the other camera chip is performed, and this affine transformation is characterized by the fact that the faces of the camera chips are congruent. Such affine transformations can always be achieved by arithmetic translations, rotations and scalings, which are actually physically implemented by optical elements in the optical system. Two chips of different size have inter alia the same pixel size and/or pixel resolution, ie the same distance between pixels. This embodiment according to the invention is particularly preferred. This is because in this embodiment the alignment marks do not even need to be projected onto the chip surface, or the outline of the camera chip can be considered as alignment marks. Further cost savings are achieved in constructing the device according to the invention, since the chip, in particular its contour itself, is the alignment mark, which eliminates the need for an alignment mark projection system. Furthermore, this makes the device according to the invention completely independent of the chip manufacturer. This is because chip manufacturers are not required to provide alignment marks, however, the chip contour is an inherent part of the structure of the alignment marks. If the contour of the chip is used as an alignment mark, the chip should be detected as centered as possible by the optical system. That is, the center of gravity of the chip should be located as close to the optical axis as possible. In particular, the distance between the optical axis and the center of gravity of the chip is less than 1 mm, especially less than 0.5 mm, more preferably less than 0.1 mm, particularly preferably less than 0.01 mm, very preferably less than 0.001 mm. .

For all previously described embodiments according to the invention in which two optical subsystems are calibrated to each other, the fact is that a perfect calibration is either impossible or not particularly desired for economic reasons. A highly accurate calibration can continue for a considerable period of time, during which other processes performed by the device cannot be performed. Generally, the calibration process can be interrupted as soon as a predefined limit is reached or exceeded. In one further extension according to the invention, it is also conceivable for the coordinates of two alignment marks that are not perfectly calibrated to each other to be stored with respect to one common coordinate system. This common coordinate system may be, for example, the lower detector coordinate system or the upper detector coordinate system. It is also conceivable that the coordinates of two alignment marks that are not perfectly calibrated to each other are stored in any other coordinate system. Therefore, the alignment marks are generally further moved and/or rotated relative to each other by a small amount after the calibration process, since a perfect overlap of the alignment marks is not achieved and/or desired. This mutual movement and/or rotation can be measured, stored and used in subsequent processes, in particular in the process of alignment of two substrates with each other, whereby the alignment determined in the substrates A correction of the coordinates of the mark is performed.

Further advantages, features and details of the invention emerge from the following description of preferred embodiments and on the basis of the drawings.

1 shows a schematic illustration, not to scale, of a first optical system according to the invention with a first optical input coupling; FIG. 1 shows a schematic illustration, not to scale, of a second optical system according to the invention with a second optical input coupling; FIG. 1 shows a schematic illustration, not to scale, of a third optical system according to the invention with a third optical input coupling; FIG. 1 shows a simplified schematic diagram, not to scale, of a first process step according to the invention; FIG. 1 shows a simplified schematic diagram not to scale of a second process step according to the invention; FIG. Figure 3 shows a simplified schematic diagram, not to scale, of a third process step according to the invention; Fig. 4 shows a simplified schematic, not to scale, of a fourth process step according to the invention; Fig. 3 shows a simplified schematic enlarged view, not to scale, of the lower sensitive surface; 1 shows a simplified schematic enlarged view, not to scale, of a fourth process step according to the invention in the starting state; FIG. 1 shows a simplified schematic enlarged view, not to scale, of a fourth process step according to the invention in a final state; FIG. 1 shows a simplified isometric schematic unfolded view, not to scale, of a first camera chip according to the invention; FIG. 1 shows a simplified isometric schematic unfolded view, not to scale, of a second camera chip according to the invention; FIG.

Identical components or components having the same function are provided with the same reference numerals in the figures.

In the illustrated figures, all optical paths 7, 7', 8 are only diagrammatically illustrated and should not be interpreted as paths strictly corresponding to the principle of an optical system. Furthermore, the optical paths 7, 7', 8 and the optical subsystems 12u, 12u', 12u'', 12o, 12o', 12o'' are reciprocal and mirror-image projected onto the camera chips 2u, 2o. not shown. This facilitates, among other things, the understanding of congruent detector coordinate systems. It will be appreciated by those skilled in the art that in a practical embodiment the mutual imaging of the camera chips 2u, 2o may and preferably be mirror images of each other. It is also clear that

FIG. 1a shows a schematic illustration, not to scale, of a first optical system 11 according to the invention, comprising two optical subsystems 12u, 12o containing two optical paths 7,8. Optical path 7 represents the illumination path of lower camera 1u to lower camera chip 2u. The optical path 8 is the imaging path of the alignment marks 9l and 9r.

The optical system 11 comprises a plurality of mirrors 3 and optical elements 4, 4', such as mirrors, lenses, prisms and the like. From light source 10 light 7 is coupled into optical system 11 . The light 7 passes through an optical system 11 comprising a mirror 3 and optical elements 4, 4', emerges again from the optical system 11 and strikes the photosensitive surface 14su of the lower camera chip 2u of the lower camera 1u.

In this first embodiment according to the invention, the light of the illumination path 7 is coupled into the optical system 11 via a light source 10 , in particular a lamp, more preferably a halogen lamp, and a mirror 3 . The light of the illumination path 7 passes through two optical systems 6o, 6u and is projected via further optical elements, in particular another mirror 3, onto the camera chip 2u of the lower camera 1u.

Of course, the incoupling of light into the optical system 11 by any other mirror 3 in the optical system 11 is also conceivable, especially if it is important to illuminate the camera chip 2o of the upper camera 1o intensively. The incoupling of light into the optical system 11 via multiple light sources 10 and multiple mirrors 3 is also conceivable.

FIG. 1a also shows an imaging path 8 which focuses the surface of or around the camera chip 2u via the optical elements 4, 4', 3 onto the camera chip 2o. image. In this particular case, camera chip 2 u represents the object plane and camera chip 2 o represents the image plane of the entire optical system 11 . In section AA two alignment marks 9l, 9r can be seen.

In a first embodiment according to the invention the alignment marks are for example the alignment marks 9l, 9r according to Fig. 4a provided directly on the photosensitive surface 14su of the lower camera chip 2u. The alignment marks 9l, 9r are here in particular collections of non-functional pixels, made in particular cross-shaped. The pixels are non-functional because they are coated, disconnected, destroyed, deactivated, or the like.

It is also conceivable that the alignment marks are alignment marks 9l, 9r according to FIG. 4b. In this case, the alignment marks 9l, 9r are not provided directly on the photosensitive surface 14su of the lower camera chip 2u, but are provided at least in the vicinity thereof. In either case the alignment marks 9l, 9r are actual physical entities.

Here, the alignment marks 9l, 9r are projected onto the upper camera chip 2o via the imaging path 8, and the alignment marks 9pl, 9pr thus projected are projected onto the photosensitive surface 14so of the upper camera chip 2o. occur. In FIG. 1a, the optical elements in the cameras 1u, 1o or the projection path 8 are already perfectly calibrated to each other, so that the projected alignment marks 9pl, 9pr at the cross-section BB are accurate and ideal. clearly appear in the correct position. In particular, it can be seen that the image plane 5u of the lower optical subsystem 12u and the object plane 5o of the upper optical subsystem 12o have a mutual distance d. The distance d has been chosen sufficiently large for the sake of clarity, but the image plane 5u as well as the object plane 5o may differ significantly from each other. In order to produce sharply projected alignment marks 9pl, 9pr, each plane of image plane 5u and object plane 5o must be located at the depth of field of the other plane.

FIG. 1b shows a schematic illustration, not to scale, of a second optical system 11' according to the invention, comprising two optical subsystems 12u', 12o' containing two optical paths 7', 8. FIG. Optical path 7' represents the illumination path of the lower camera 1u to the lower camera chip 2u. In this embodiment according to the invention, the light of the illumination path 7' is not coupled via the light source 10, but simply from the surroundings, in particular directly, into the optical system 11'. The light is scattered light that can enter the optical system 11' by deliberately not installing a corresponding shielding of the optical system 11', especially at least in one place, more preferably at the camera 1u. . The in-coupling of light into the optical system 11' from any other point in the optical system 11', in particular at the mirror 3, is also conceivable. In-coupling of light at multiple points in the optical system 11' is also conceivable. Alternatively, it is also conceivable to provide illumination around the camera, in particular with LEDs as light sources.

FIG. 1b also shows an imaging path 8 which focuses the surface of or around the camera chip 2u via the optical elements 4, 4', 3 onto the camera chip 2o. image. In this particular case, camera chip 2u represents the object plane and camera chip 2o represents the image plane. Sections AA and BB show the optimum imaging situation, as already explained in FIG. 1a.

FIG. 1c shows a schematic illustration, not to scale, of an optical system 11'', consisting of two optical subsystems 12u'', 12o'' containing two optical paths 7'', 8. FIG.

The optical path 7'' is formed in the first embodiment according to the invention by alignment marks 9l, 9r on the surface 19, which at the same time also serve as the light source 10 (Fig. A - see A). For example, it is also conceivable for the alignment marks 9l, 9r to consist in particular of cross-shaped LED fields.

In another second embodiment according to the invention, the surface 19 on which the alignment marks 9l, 9r are provided emits light, the alignment marks 9l, 9r not functioning as active light sources 10, but merely Acts as a mask. In this case the alignment marks 9l, 9r are projected through the illumination path 7'' as shadow marks.

An embodiment according to the invention projects the alignment marks 9l, 9r of the surface 19 onto the camera chip 2u (see Figures BB). Photosensitive surface 14su of camera chip 2u again represents the object plane for camera 1o. That is, the alignment marks 9l′ and 9r′ projected by the alignment mark projection system 21 are projected as alignment marks 9pl and 9pr onto the photosensitive surface 14so of the upper camera chip 2o of the upper camera 1o via the optical system 11″. be done.

The difference with the embodiment according to FIGS. 1a and 1b is that neither of the two camera chips 2u, 2o has to have its own alignment marks 9l, 9r, instead their alignment marks 9l , 9r are projected onto the photosensitive surface 2u of the lower camera 1u as projected alignment marks 9l′ and 9r′ via the alignment mark projection system 21 according to the invention and thus introduced into the optical system 11″. It is a point.

In FIGS. 1a to 1c the ideal situation can be seen in that the optical elements 3, 3o, 3u, 4, 4′, 6u, 6o, 1u, 1o are already perfectly aligned with each other. It is shown. In the further figures 2a to 2d and 3a, 3b the individual process steps that must be performed to achieve this ideal situation and calibrate the optical system 11, 11', 11'' are shown. Have been described. In particular, the optical paths, in particular the illumination paths 7, 7' and imaging paths 8 and most of the optical elements have been omitted for clarity of the drawing. FIGS. 2a to 2d illustrate, by way of example and representative, the optical system 11 described in FIG. 1a. FIG. 2a shows a simplified schematic, not to scale, of an optical system 11 according to the invention in a first process step 101 according to the invention, consisting of two optical subsystems 12u, 12o as described in FIG. 1a. A characteristic feature in this figure is in particular the distance d between the lower image plane (also called optical surface) 5u of the lower optical system 6u and the upper image plane 5o of the upper optical system 6o.

The alignment marks 9l and 9r are provided on the photosensitive surface 14su with a distance dx in the x direction and a distance dy in the y direction from each other.

The distance d between the optical surface 5u and the optical surface 5o is such that the upper optical surface 5o does not cross the lower depth of field tu of the lower optical surface 5u, or the lower optical surface 5u does not cross the upper depth of field tu of the upper optical surface 5o. It has a size that does not cross the depth to. Optical surface 5u is the image plane of lower optical subsystem 12u.

However, the alignment marks 9l, 9r projected onto the image plane 5u must be projected onto the photosensitive surface 14so of the upper camera chip 2o via the upper optical subsystem 12o. However, in order to form a clear image of the alignment marks 9l and 9r projected onto the image plane 5u of the lower optical system 12u on the photosensitive surface 14so, the optical surface 5u must be located within the depth of field to of the upper optical surface 5o. and this upper optical surface 5o simultaneously represents the object plane for the upper optical subsystem 12o. As shown in FIG. 2a, the projected alignment marks 9pl, 9pr would otherwise be imaged poorly on the photosensitive surface 14so (see FIGS. BB). That is, the key to the process step of FIG. 2a is to bring the two optical surfaces 5u and 5o close to each other.

FIG. 2b shows a simplified schematic, not to scale, of the optical system 11 in a second process step 102 according to the invention, consisting of two optical subsystems 12u, 12o, here optical surfaces 5u and The optical surfaces 5o are sufficiently close to each other, while the optical axis 13u of the optical system 6u and the optical axis 13o of the optical system 6o are sufficiently large relative to each other so that they do not cross between the optical systems 6u, 6o. are displaced.

Due to this large deviation of the optical axes 13u, 13o, only the alignment mark 9pl is present in the field of view of the upper camera 1u (see Figure BB). Since a part of the optical surface 5u on which the alignment mark 9l is temporarily projected is positioned at the depth of field to with respect to the upper optical surface 5o, the alignment mark 9l is clearly imaged.

As a result of the optical axis 13u and optical axis 13o being offset from each other, the projected image including the alignment marks 9pl and 9pr on the upper photosensitive surface 14so of the upper camera chip 2o is shifted. This deviation can be so large that one of the alignment marks 9pl, 9pr is not projected onto the photosensitive surface 14so, so that one of the alignment marks is not visible. Here, the invisible alignment mark is the alignment mark 9pr. That is, what is important in the process step of FIG. 2b is to bring the two alignment marks 9pl, 9pr into the field of view of the top camera 1o.

FIG. 2c shows a simplified schematic, not to scale, of the optical system 11 in a third process step 103 according to the invention, consisting of two optical subsystems 12u, 12o, here two projected The alignment marks 9pl, 9pr are indeed present in the field of view of the upper camera 1o, although the two optical surfaces 5u and 5o are still highly tilted with respect to each other. Here, a portion of the lower optical surface 5u is positioned within the upper depth of field to of the upper optical surface 5o, and the other portion is positioned outside the upper depth of field to.

Accordingly, following similar considerations to the description of FIG. 2b, alignment mark 9l is sharply imaged as alignment mark 9pl, whereas alignment mark 9r is imaged dimly as alignment mark 9pr. Optical surfaces 5u and 5o such that by corresponding movement of lower optical subsystem 12u and/or upper optical subsystem 12o, in particular optics 6u, 6o, any projected alignment marks 9pl and 9pr are clearly represented. can be aligned with each other.

From the above description, it can be arithmetically derived how to calculate the minimum wedge error that can be barely measured and therefore adjusted with the method according to the invention. For the sake of clarity, it is assumed for the calculations that the two optical surfaces 5u, 5o are tilted only about a tilt axis 20 parallel to the x-axis. To is the depth of field of the upper optical surface 5o, and dx is the distance between the alignment marks 9l and 9r. in this case,
tan α = t _o /d _x
holds.

Therefore, the minimum correctable wedge error is
α = arctan(t _o /d _x )
is.

It can be seen that the correctable wedge error decreases as the distance dx between the alignment marks 9l and 9r increases and as the depth of field to of the upper optical surface 5o decreases. That is, what is important in the process step of FIG. 2c is to sufficiently minimize the wedge error between the two optical surfaces 5u, 5o.

FIG. 2d shows a simplified schematic diagram, not to scale, of the optical system 11 in a fourth process step 104 according to the invention, consisting of two optical subsystems 12u, 12o, in an optimal state, here , the optical surface 5u representing the image plane for the projected alignment marks 9l and 9r is located at the depth of field to of the upper optical surface 5o, which at the same time is the upper optical subsystem 12o and thus the object plane for the projected alignment marks 9pl and 9pr. In particular, the two faces 5u and 5o are parallel to each other. In practice, however, the two surfaces always have an angle with each other that is never zero. Here, the angle between the two surfaces 5u, 5o is less than 5°, in particular less than 1°, more preferably less than 0.1°, particularly preferably less than 0.01°, very preferably 0.001 ° is less than Those skilled in the art will recognize that the angle between two surfaces is the same as the angle between two surface normals.

Since the lower optical surface 5u is located at the depth of field to of the upper optical surface, the alignment marks 9l and 9r are imaged as sharp alignment marks 9pl and 9pr (see Figures BB). .

In this process step, a more precise calibration of the alignment marks 9pl, 9pr is performed with reference to the desired ideal positions 9il, 9ir (see Fig. 3b). It is thus important in the process step of FIG. 2d to perform a precise calibration of the alignment marks 9pl, 9pr, especially in the x- and/or y-direction.

FIG. 3a shows a simplified schematic enlarged view, not to scale, of the photosensitive area 14su of the lower camera chip 2u. Corresponding alignment marks 9l, 9r can be seen. The position of the alignment marks 9l, 9r can best be described with reference to the lower detector coordinate system (xdu, ydu). The origin of the lower detector coordinate system (xdu, ydu) is located, for example, at the upper left corner of the photosensitive surface 14su.

FIG. 3b shows a simplified schematic enlarged view, not to scale, of the photosensitive area 14so of the upper camera chip 2o at the start of the fourth process step 104 according to the invention.

It can be seen that the projected alignment marks 9pl, 9pr are not congruent with the ideal positions 9il, 9ir. The upper photosurface 14so has an upper detector coordinate system (xdo, ydo). The origin of the upper detector coordinate system (xdo, ydo) is located at the upper left corner of the photosurface 14so.

The coordinates of the ideal positions 9il, 9ir in the detector coordinate system (xdo, ydo) are such that, inter alia, the photosensitive areas 14su, 14so have the same properties, e.g. length, width, resolution in the x direction, resolution in the y direction, etc. As long as, or in short, the same camera chips 2u, 2o are used, it corresponds to the coordinates of the alignment marks 9l, 9r in the lower detector coordinate system (xdu, ydu). Another condition, of course, is to choose the origins of the detector coordinate systems (xdu, ydu) and (xdo, ydo) exactly and always identically.

A further adaptation of the optical elements in the optical system 11, 11', 11'' allows the alignment marks 9pl, 9pr to be calibrated with reference to the ideal positions 9il, 9ir. At this time, translational movement and/or rotation of the alignment marks 9pl and 9pr can be caused with reference to the detector coordinate system (xdo, ydo).

Alignment marks 9pl, 9il or 9pr, 9ir may be completely congruent with each other if it is not economically desirable because full calibration is not possible at all and/or takes too long. rather than being moved relative to each other by translational and/or rotational motion. The alignment process will end at this step. According to the invention, the system stores the coordinates of the alignment marks 9pl, 9il, 9pr, 9ir with reference to the detector coordinate system (xdo, ydo). An optical system so calibrated is used in a subsequent process such that, for example, a first alignment mark on a first substrate surface of a first substrate aligns with a second alignment mark on a second substrate surface of a second substrate. When used to have alignment marks to be mutually aligned, measured and stored translational and/or rotational movements must be used for correction.

FIG. 3c shows a simplified schematic enlargement, not to scale, of the photosensitive area 14so of the upper camera chip 2o at the end of the fourth process step 104 according to the invention. Alignment marks 9pl, 9pr are located at ideal positions 9il, 9ir. The optical system 11, 11', 11'' is thus calibrated. Although the above-mentioned preferred aim of the process according to the invention is to bring the projected alignment marks 9pl, 9pr congruent with the ideal positions 9il, 9ir, the projected alignment marks 9pl, 9pr instead of congruent with the ideal positions 9il, 9ir, but instead by rotational and/or translational movements between the projected alignment marks 9pl, 9pr and the ideal positions 9il, 9ir. The possibility of storing movements is disclosed. With this stored information, coordinate corrections and/or image corrections can be performed at any time. Performing such coordinate corrections and/or image corrections is associated with computational power. Due in particular to tolerances in the optical and/or mechanical components of the optical system 11, 11', 11'', the alignment marks 9pl, 9pr may be completely congruent with the ideal positions 9il, 9ir. It is also conceivable that it is not possible to In this case, the movement by rotational movement and/or by translational movement, inter alia, is likewise stored. Coordinate corrections and/or image corrections should always be performed, inter alia, to obtain the most accurate results possible.

FIG. 4a shows a not-to-scale isometric schematic exploded view of the disassembled camera chip 2u according to the first embodiment of the invention. The camera chip 2u consists of a chip carrier 14 with a photosensitive surface 14su.

Chip carrier 14 is usually sealed by a protective plate 15, in particular a glass plate. In this case, the sealing will crack under extreme force, usually destroying the chip carrier 14, especially the photosensitive surface 14su. Alignment marks 9l, 9r must therefore be made by the chip manufacturer, inter alia, prior to sealing by protective plate 15 .

A further glass plate 16, in particular an optical filter, can be attached and fixed to the protective plate 15. FIG. In most cases all components 14 , 15 , 16 are fixed by a frame 17 .

FIG. 4b shows a not-to-scale isometric schematic exploded view of an exploded camera chip 2u according to another embodiment of the invention, here a separate chip according to the invention with alignment marks 9l, 9r. is fixed directly following the protective plate 15, ie as close as possible to the photosensitive surface 14su. In particular, the alignment marks 9l, 9r are provided on the side of the marking plate 18 facing the photosensitive surface 14su in order to further shorten the distances between the alignment marks 9l, 9r and the photosensitive surface 14su.

Insertion of the marking plate 18 can be implemented relatively easily in most camera chips 2u. This is because all the components above the protective plate 15 can be removed easily and even specifically intentionally. This allows a camera chip 2u of this kind to be extended in particular by filters and in special cases by a marking plate 18 .

1o, 1u cameras 2o, 2u camera chips 3, 3o, 3u mirrors 4, 4' lenses 5o, 5u optical surfaces, in particular object or image planes 6o, 6u optics 7, 7', 7'' illumination paths 8 imaging Paths 9l, 9r, 9l', 9r' Alignment Marks 9pl, 9pr Projected Alignment Marks 9il, 9ir Ideal Alignment Marks 10 Light Sources 11, 11', 11'' Optical System 12u, 12u', 12u'' Optical Sub System 12o, 12o', 12o'' optical subsystem 13u, 13o optical axis 14 chip carrier 14so, 14su photosensitive surface 15 protective plate 16 glass plate, in particular filter 17 frame 18 marking plate 19 surface 20 tilt axis 21 alignment mark projection system α Angle between optical surfaces AA Sectional view BB Sectional view d Distance dx, dy Distance tu, to Depth of field xdu, ydu Coordinates

Claims (16)

a first optical subsystem (12u, 12u', 12u'') and a second optical subsystem (12o, 12o' ) of an optical system (11, 11', 11'') arranged oppositely , 12o''), comprising:
projecting alignment marks (9l, 9r, 9l', 9r') onto a first optical surface ( 5u) of said first optical subsystem ( 12u, 12u', 12u'');
From the first optical surface ( 5u) to the sensitive surface (14so) of the second optical subsystem ( 12o, 12o', 12o''), the alignment marks (9l, 9r, 9l', 9r') and projecting
aligning said first optical subsystem (12u, 12u', 12u'') and said second optical subsystem (12o, 12o', 12o'') with respect to each other, whereby said sensitive surface ( imaging the projection (9pl, 9pr) of said alignment mark (9l, 9r, 9l′, 9r′) at a depth of field of 14so) to an ideal position (9il, 9ir);
A method. Light (7) for illuminating the alignment marks (9l, 9r) is transmitted through at least one light source (10 ) and at least one mirror (3) to the first optical subsystem (12u , 12u′, 12u″) and/or the second optical subsystem (12o, 12o′, 12o″). The alignment mark ( 9l, 9r) for incoupling ambient light (7') for illuminating said first optical subsystem (12u, 12u', 12u'') and said second optical subsystem ( 12o, 12o); 3. The method according to claim 1 or 2, wherein the shielding of ', 12o'') is not installed. The alignment marks ( 9l ', 9r') comprising LED fields and/or formed as masks are projected onto the first optical subsystem (12u, 12u', 12u ) by an alignment mark projection system (21). '') onto a first sensitive surface (14su) of a first camera chip (2u) of a first camera (1u) arranged in '') . Method. Said first optical subsystem (12u, 12u', 12u'') and said second optical subsystem ( 12o, 12o', 12o'') are arranged in a first optical system ( 6u) and a second optical system (6o), a first optical surface (5u) of said first optical system (6u) and a second optical surface of said second optical system (6o) 5. Method according to claim 4 , wherein (5o) and /or optical axes (13o, 13u) are aligned with each other. 6. Method according to claim 5, wherein at least said first optical system (6u) and second optical system (6o) are part of an apparatus for aligning substrates . Alignment marks (9l, 9r) are arranged near and/or on the first sensitive surface (14su) of the first camera chip (2u) of said first camera (1u) and/or projecting alignment marks (9l', 9r') onto the first sensitive surface (14su) of the first camera chip (2u) of the first camera (1u);
From said first camera chip (2u), through said first optical subsystem (12u, 12u', 12u'') having a first optical system (6u), said first optical projecting said alignment marks (9l, 9r, 9l', 9r') onto said first optical surface (5u) arranged between a system (6u) and a second optical system (6o) ;
from said first optical surface (5u) through said second optical subsystem (12o, 12o', 12o'') comprising a second optical system (6o) to said second optical said alignment marks ( 9l , 9r, 9l′, 9r′);
7. A method according to claim 5 or 6, comprising 8. The claim 5, 6 or 7, wherein the first optical system (6u) and the second optical system (6o) are moved for the alignment by mutual translational and/or rotational movements. Method. The first optical system (6u) and the second optical system (6o) are arranged so that the first optical surface (5u) of the first optical system (6u) is aligned with the second optical system (6u) for the alignment. 9. A method according to claim 5, 6, 7 or 8, wherein the second optical surface (5o) of the optical system (6o) is approximated to lie in the depth of field to. Any of claims 5 to 9, wherein the alignment marks (9l, 9r) are provided directly on the first sensitive surface (14su) of the first camera chip (2u) of the first camera (1u). or the method according to item 1. Claims 5 to 10, wherein said alignment marks (9l, 9r) comprising a collection of non- functional pixels are provided directly on the first sensitive surface (14su) of said first camera chip (2u). A method according to any one of . Said alignment marks (9l, 9r) are provided on a separate marking plate (18) in a first camera chip (2u) of said first camera (1u), said alignment marks (9l, 9r) and Method according to any one of claims 5 to 11, wherein the distance of said first camera chip (2u) to the first sensitive surface (14su) is less than 1 mm. a first optical subsystem (12u, 12u', 12u'') and a second optical subsystem (12o, 12o' ) of an optical system (11, 11', 11'') arranged oppositely , 12o'') by a method according to any one of claims 1 to 12, in a system (11, 11', 11'') comprising:
A first camera chip ( 2u) with a first camera (1u);
Projecting said alignment marks (9l, 9r, 9l', 9r') from the first optical surface (5u) onto the sensitive surface (14so) of the second optical subsystem ( 12o, 12o', 12o'') means to
aligning said first optical subsystem (12u, 12u', 12u'') and said second optical subsystem (12o, 12o', 12o'') to each other, whereby said sensitive surface (14so) means capable of imaging projections (9pl, 9pr) of said alignment marks (9l, 9r, 9l', 9r') at a depth of field of
A system (11, 11', 11'') having Said alignment marks ( 9l ', 9r') comprising LED fields and/or formed as masks are projected by an alignment mark projection system (21) onto the first camera chip ( 14. The system (11, 11', 11'') according to claim 13, projected onto the first sensitive surface (14su) of 2u). Camera having alignment marks (9l, 9r) near and/or on the sensitive surface (14su) of the camera chip for use in a method according to any one of claims 1 to 12 Chip (2u). Alignment marks (9l, 9r) near and/or on the sensitive surface (14su) of the camera chip for use in a system (11, 11', 11'') according to claim 13 or 14 camera chip (2u) with.

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